1. Field of the Invention
This invention relates to an apparatus and a method for manufacturing non-metallic laminate materials and, more particularly, to a device and method to manufacture nonmetallic turbine engine components.
2. Description Of the Prior Art
There is a continual demand to design turbine engine components such as used on jet aircraft of lighter weight materials to increase the aircraft's fuel efficiency and thrust capabilities. Originally, many jet aircraft components were made of steel. Then, lighter weight, high strength aluminum components replaced many of the steel components. Subsequently, titanium components replaced many of the aluminum components further decreasing the weight of the aircraft components. Recently, with the advent of high strength, non-metallic composite materials, such as graphite fibers embedded within a polyimide resin, the titanium components have been replaced with the lighter weight, nonmetallic materials. One example is the bypass duct of the General Electric F404 Augmented Turbofan Engine.
However, the composite materials generally are difficult to mold into properly shaped parts. For example, graphite-polyimide materials are generally characterized by poor handling characteristics, erratic processing response, highly variable molded product quality due to porosity and high shrinkage that can cause micro-cracking and/or delamination of complex contoured parts. This results in high rejection rates for composite parts, expensive labor costs to correct problems and/or expensive molds to obtain a properly dimensioned part.
FIGS. 1-4 disclose three prior art molding systems for molding the bypass ducts of the F404 Engine. FIGS. 1 and 2 show a prior art female mold system 10 used for molding a one-half section of a composite bypass duct. The mold system 10 includes a female mold 12 having an inner portion 14, an outer portion 16, an upper portion 18 and a lower portion 20. Further, the female mold 12 includes flange offsets 22 and 24.
The manufacture of a composite duct will now be discussed. First, a plurality of sheets or plies 25 of resin coated composite material, such as the graphite-polyimide material sheets, are placed on an outer surface 26 of the inner portion 14, forming an initial laminated flange, which is substantially semi-circular in cross-section. Typically, a plurality of plies 25 are first laid on top of each other forming the initial laminated duct section 30. Each ply has a thickness of 12.5 to 15.5 mils, and sufficient plies are utilized to form the necessary thickness, up to 50 plies thick if necessary.
Second, the mold is heated to, for example, 100.degree. F.-150.degree. F. This causes the plies 25 to debulk and to adhere to one another, forming a preliminary laminated duct section 30. The preliminary laminated duct section 30 is porous at this point and requires further compacting to eliminate the excessive porosity. Excessive porosity affects the strength and dimensional characteristics of the parts, such as size and tolerances.
Third, a bag system 40, which is well-known in the art, is placed on an outer surface 42 of the preliminary laminated duct section 30. The bag system 40 conforms to the outer surface 42 of the preliminary duct section 30.
Fourth, the mold system 10 is placed in an autoclave. The bag system is attached to a vacuum source, then the autoclave is pressurized and heated. This compacts the preliminary laminated duct section 30 into its final form and eliminates the porosity problem. Two final-form laminated duct sections are attached to each other in this manner forming a bypass duct for a jet engine.
FIG. 3 shows a prior art male mold system 50 used for molding a bypass duct of an engine. System 50 includes a cylindrical male mold 52 having a cylinder portion 54 and two flange portions 56. Flange restraining plates 58 abut respective flange portions 56.
The manufacture of a composite duct using system 50 will now be discussed. A plurality of sheets or plies 60, similar to plies 25, are laid one on top of each other, and placed on an outer surface 62 of the male mold 52 forming an initial laminated cylindrical duct 65. The mold 52 is then heated to a temperature in the range of about 125.degree. F. to 150.degree. F. This causes the plies 60 to debulk and to adhere to one another, forming a preliminary porous laminated duct 65. Like the preliminary duct section 30, the preliminary duct 65 requires further compacting to eliminate the porosity problem. A bag system 70, similar to bag system 40, is placed on an outer surface 72 of the duct 65 after restraining plates 58 are positioned to reduce wrinkling at the corners. The mold system 50 is then placed in an autoclave and the preliminary laminated duct 65 is compacted into its final shape while simultaneously eliminating the excessive porosity.
FIG. 4 shows a prior art compound male mold system 80 that includes a cylindrical exterior mold 82 having a flange 84 and an interior mold 86 having a flange 88. The exterior male mold 82 slideably receives the interior mold 86. Cauls 90 attach to respective flanges 88 and 84. A plurality of sheets or plies 92, similar to plies 25, are laid one on top of each other adjacent to exterior surfaces of the respective mold parts 82, 86, forming an initial laminated duct 94 similar to duct 65. The molds 82 and 86 are then heated, enabling the plies 92 to adhere to one another, forming a preliminary porous laminated duct. A bag system 96 is placed on an outer surface of the preliminary duct 94. The mold system 80 is then placed in an autoclave, as previously discussed for the other systems 10 and 50, and results in a final duct shape. Mold system 80 provides for a more uniform compaction of the duct flange than mold system 50 because the molds 82 and 86 slideably expand as a function of temperature.
Each of the above-identified systems 10, 50, 80 has drawbacks. The female system 10 forms a duct having properly dimensioned flanges; however, it is an expensive system to operate. The male system 50 forms flanges that lack optimal flange strength and may require subsequent labor-intensive repairs to correct; however, its advantage is that it is inexpensive to operate relative to the female system 10. The male system 80 overcomes the problem of optimization of flange strength of system 50; however, it is expensive to operate due to the cost of the special mold. Additionally, in the systems depicted in both FIG. 3 and FIG. 4, rejection rates are high because of the difficulty in controlling the porosity of the laminate material.
Further, general problems exist with the bag systems such that localized pressure cannot be applied to specific areas of the molded material. The resin tends to squeeze out during curing resulting in a dry unacceptable laminate. The laminated part thickness also tends to vary from part to part because of the difficulty in controlling the process. Another undesirable problem is that upper and lower flange surfaces tend to need extensive subsequent machining because they are nonparallel.
Therefore, it is an object of our invention to provide an apparatus and a method for inexpensively molding composite materials and overcome the deficiencies of the bag systems.
It is a further object of our invention to provide an apparatus and method for manufacturing a composite component resulting in lower rejection rates than that of the prior art.
It is another object of the present invention to provide a more compacted flange having flange surfaces which require less machining because they are closer to being parallel.